Compressed file system for non-volatile RAM

ABSTRACT

Methods and arrangements are provided that significantly reduce or otherwise minimize the amount of NVRAM required within a given computing device. For example, a novel data structure and management scheme are provided in a manner that allows an NVRAM sector-based memory to appear as providing significantly more storage space than it physically has. This is accomplished by mapping a higher number of virtual sectors to a fewer number of physical sectors. Data written to a plurality of virtual sectors is compressed and written to physical sector(s). The information needed to associate the virtual and physical sectors can be maintained in a virtual sector table within less expensive RAM. If power is lost and the virtual sector table is no longer available in the RAM, then on power-up the virtual sector table is recreated based in information that is imbedded within the stored data structure in physical sectors of the NVRAM. The scheme promotes data integrity by carefully controlling the compression and decompression processes and providing data and operational step backup information to insure that data within the NVRAM is not lost by a sudden power loss, etc.

CROSS REFERENCE TO RELATED PATENT APPLICATION

This is a continuation of and priority is claimed to co-pending U.S.Patent Application having Ser. No. 09/560,838 and a filing date of Apr.28^(th), 2000 for COMPRESSED FILE SYSTEM FOR NON-VOLATILE RAM of Shoffet al. This co-pending U.S. Patent Application is commonly assignedherewith and is hereby incorporated herein by reference for all that itdiscloses.

TECHNICAL FIELD

This invention relates generally to data storage mechanisms and, moreparticularly, to methods and arrangements for providing a compressedfile system in non-volatile random access memory (NVRAM) or other likedata storage mechanism.

BACKGROUND

During normal operations, information is stored within a computingdevice in the form of data. For example, in a typical personal computer(PC) data can be temporarily stored in a system or primary memoryconsisting of random access memory (RAM). Further data may be stored ina secondary memory, such as, a hard drive, a floppy drive, opticaldrive, etc. In such configurations, the secondary memory provides anon-volatile data storage alternative to the primary memory since thedata stored in the primary memory would usually be lost if a powerfailure occurred. Solid-state non-volatile RAM (NVRAM), which is capableof retaining the stored data even after a power failure, is currentlyavailable but tends to be cost prohibitive for most PCs.

There are some computing devices, however, that can benefit from the useof NVRAM. One example is a set top box (STB) that is used to provideentertainment and related information services to subscribing users.Very little data storage is typically needed to provide such services,as compared to a full-fledged PC application. Thus, all or part of theprimary memory in the STB can be NVRAM. This essentially eliminates theneed to provide a secondary memory, such as, a hard drive, or the like.This can reduce the overall complexity, size and cost of the STB, forexample.

Since NVRAM tends to be relatively expensive when compared to RAM and/orconventional secondary memory, there is an attendant need tosignificantly reduce or otherwise minimize the amount of NVRAM requiredwithin a given computing device.

SUMMARY

Methods and arrangements are provided that significantly reduce orotherwise minimize the amount of NVRAM required within a given computingdevice.

For example, a novel data structure and management scheme are providedin a manner that allows an NVRAM sector-based memory to appear asproviding significantly more storage space than it physically has. Thisis accomplished by mapping a higher number of virtual sectors to a fewernumber of physical sectors. Data written to a plurality of virtualsectors is compressed and written to physical sector(s). The informationneeded to associate the virtual and physical sectors can be maintainedin a virtual sector table within less expensive RAM. If power is lostand the virtual sector table is no longer available in the RAM, then onpower-up the virtual sector table is recreated based in information thatis imbedded within the stored data structure in physical sectors of theNVRAM. The scheme promotes data integrity by carefully controlling thecompression and decompression processes and providing data andoperational step backup information to insure that data within the NVRAMis not lost by a sudden power loss, etc.

The above stated needs are met, for example, by a method that includesreceiving file system data from an operating system, storing the filesystem data in a plurality of reserved sectors within a non-volatilememory, compressing the file system data stored within in the pluralityof reserved sectors to create a compressed data block, and storing thecompressed data block in at least one physical subsector within thenon-volatile memory. In this manner the operating system can be providedwith a plurality of operatively accessible virtual sectors resulting ina virtual memory capacity that exceeds the actual physical capacity ofthe non-volatile memory.

The method may further include, therefore, mapping the plurality ofvirtual sectors to at least one physical subsector through a VirtualSector Table (VST) stored in a volatile memory and presenting theoperating system with the VST. A Sector Allocation Table (SAT) withinthe volatile memory can be used to map physical subsectors to the VST.The SAT can be generated based at least on a unique group identifierthat is stored in each physical subsector associated with storing thecompressed data block. For example, the SAT can be generated during adevice initialization time.

The step of storing the compressed data block in at least one physicalsubsector within the non-volatile memory may further include associatingeach physical subsector with a unique group identifier. The step ofstoring the compressed data block in at least one physical subsectorwithin the non-volatile memory may further include writing each physicalsubsector associated with the compressed data block to the non-volatilememory in an a sequential order, but not necessarily a contiguous order.

In still other implementations, the step of storing the compressed datablock in at least one physical subsector within the non-volatile memoryfurther includes, maintaining input/output (I/O) operation statusinformation within the non-volatile memory, during on-going I/Ooperations, that identifies the status of on-going I/O operations withrespect to data stored within non-volatile memory.

An arrangement for use in providing an application access to anon-volatile memory is also provided. The arrangement includes anoperating system and a device driver. Here, the operating system isconfigured to exchange input/output (I/O) requests with the applicationand exchange corresponding file system requests with the device driver.The device driver is configured to store the file system data receivedfrom the operating system in a plurality of reserved sectors within thenon-volatile memory, compress the file system data stored within in theplurality of reserved sectors to create a compressed data block, andstore the compressed data block in at least one physical subsectorwithin the non-volatile memory. This arrangement can be included alongwith a processor configured to run the operating system and the devicedriver, and a non-volatile memory that is operatively coupled to theprocessor as part of a set top box or other like computing device.

A non-volatile computer-readable medium having stored thereon a datastructure, is also provided. The data structure includes a raw sectormap data and a plurality of raw sectors as identified in the raw sectormap that are configurable to store uncompressed data during input/output(I/O) operations, I/O operation status data identifying on-going I/Ooperation, and a plurality of subsectors contiguously arranged andconfigured to support the identified on-going I/O operations by storingcompressed data blocks derived from the uncompressed data.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the various methods and arrangements ofthe present invention may be had by reference to the following detaileddescription when taken in conjunction with the accompanying drawingswherein:

FIG. 1 is a block diagram depicting an exemplary computing device havinga non-volatile random access memory (NVRAM).

FIG. 2 is a block diagram depicting an exemplary functional arrangementof a computing device as in FIG. 1.

FIG. 3 is a functional block diagram depicting an arrangement forcompressing file system data into an NVRAM as in FIG. 1.

FIG. 4 is an illustrative diagram depicting the layout of an NVRAM as inFIG. 1.

FIG. 5 is an illustrative/functional block diagram file system databeing compressed and stored in an NVRAM as in FIG. 1.

DETAILED DESCRIPTION

The following description describes various methods and arrangementsthat are implemented in a computing device running Microsoft® Windows®CE. This is by way of example only. Those skilled in the art willclearly recognize that the various methods and arrangements as describedbelow and shown in the Drawings can be used in any type of computingdevice having any type of operating system that is configured toread/write data from/to a non-volatile memory arrangement.

Windows® CE is a scalable operating system (herein after, referred to asthe “OS”) that is designed for a variety of embedded systems andproducts. Its multithreaded, multitasking, fully preemptive operatingenvironment is designed specifically for hardware with limitedresources, such as consumer electronic devices, specialized industrialcontrollers, and embedded communications devices. The OS also supportsvarious hardware peripherals, devices, and networking systems. Theseinclude keyboards, mouse devices, touch panels, serial ports, Ethernetconnections, modems, universal serial bus (USB) devices, audio devices,parallel ports, printer devices, and storage devices, such as PC Cards.

With this in mind, FIG. 1 is a functional block diagram depicting anexemplary computing device 20 having at least one processor 22 that isoperatively coupled to a memory 24 through at least one bus 26.Processor 22 is further operatively coupled to at least one input/outputdevice 28 through bus 26. In this example memory 24 includes read onlymemory (ROM) 30, non-volatile random access memory (NVRAM) 32, andrandom access memory (RAM) 34. During normal operations, a sectorallocation table (SAT) 36, a virtual sector table (VST) 38 and a GroupID table 40 are generated and stored in RAM 34. These tables and theinformation in them are described in greater detail in subsequentsections. Those skilled in the art will recognize that computing device20 may be implemented through the use of one or more integratedcircuits, etc.

FIG. 2 is a functional block diagram depicting an exemplary functionalarrangement 60 of computing device 20, for example, as in FIG. 1. Here,an application program 62 is operatively configured to interface with anoperating system (OS) 64 and support reading and writing operations to amemory. OS 64 is in turn operatively configured to interface with adevice driver, in this case, a block device driver, that furthersupports the read/write operation.

Block device drivers are provided for data storage devices that allowdata to be read or written only in blocks of a fixed size. Block devicesdo not allow individual bytes of data to be read or written. Block sizestend to be one or a few kilobytes; some common sizes are 512 bytes, 1KB, 2 KB, and 4 KB. Block devices are ideally suited to mass storage andpersistent storage applications, such as disk and tape drives, or NVRAM.

As shown in FIG. 2, OS 64 includes a FAT File System (FATFS) 66 tosupport an “NVFile” device driver 68. FATFS 66 essentially implements alogical file system and provides an abstraction between files in theapplication name space and devices in the device name space. Forexample, FATFS can exchange “Read File ( )” 70, “Write File ( )” 72 and“IOCTL_DISK_FORMAT_VOLUME 74, as applicable, with application 62. Thenon-volatile file (“NVFile”) device driver 68, in this example a blockdevice driver, is responsible for guaranteeing safe I/O operations evenwhen device 20 is interrupted by a power cycle. NVFile 68 exchanges aread request “DISK_IOCTL_READ” 76 and write request “DISK_IOCTL_WRITE”78, as applicable, with FATFS 66. In the above example, both FATFS 66and NVFile 68 are implemented as data link lists (e.g., dll modules).

NVFile device driver 68 creates a storage device of NVRAM 32 to persistraw data from the FATFS file system. As described herein, it is possibleand advantageous to extend the available storage space by compressingfile system data into NVRAM 32. This can be accomplished without makingsubstantial changes to the FATFS layer supplied by the core OS 64.

The successful implementation of a compressed file system as describedherein takes advantage of conventional software compression schemes,such as the LZX library from the OS. This exemplary software compressionscheme tends to yields an average compression ratio of approximately4:1.

The NVFile storage device in this example can be addressed by FAT-12implementation using 512-byte sectors, and one sector per cluster, forexample. Here, FATFS 66 notifies its underlying block device driverNVFile 68 when formatting or file (cluster) delete operations occur.FATFS 66 also performs a low-level format whenever a media formatoperation is performed. Communication between FATFS 66 and NVFile 68insures correct reporting of “disk full” status and the existence offree space. For example, FATFS 66 notifies NVFile 68 when clusters aredeleted, to insure that free space is reported accurately and freeclusters can be properly identified as free space.

Reference is now made to FIG. 3, which is a functional block diagramdepicting an arrangement for compressing file system data into NVRAM 32as in FIG. 1. As depicted, FATFS 66 provides a write request (78) thatspecifies a buffer 4“pData” (e.g., a block of data) and a “Sector XXX”.Sector XXX is then mapped to a “virtual sector” within VST 38. Since theactual physical storage capacity of NVRAM 32 is less than that supportedby VST 38, a compression stage 80 is introduced in NVFile to compressthe “pData” and store a corresponding compressed block of data on NVRAM32.

This process saves NVRAM for data and is designed to avoid wastingvaluable NVRAM by persisting too much organizational information ortables of pointers. Thus, in this example, tables and pointers arealmost exclusively maintained in RAM 34 rather than in NVRAM 32.Nevertheless, atomic/safe operations are provided to maintain data andorganizational integrity across power-cycles. As will be appreciated,the methods and arrangements presented herein also tend to avoid heapfragmentation.

FIG. 4 is an illustrative diagram depicting an exemplary layout of NVRAM32. Here, NVRAM 32 includes a raw sector map 100, an I/O operationstatus 102, a plurality of reserved raw sectors 104 (numbered 0-6), anda plurality of subsectors 106 (numbered 0-N).

Let us assume, in this example, that NVRAM 32 is a 100-k byte memorywithin a set top box. Here, the beginning of the 100-k block of NVRAM 32starts with a 28-byte raw sector map 100 (one DWORD for each reservedsector), then a series of seven 512-byte raw uncompressed reservedsectors 104. Following the end of the reserved sectors 104 are the128-byte subsectors 106 to store compressed blocks of data from the filesystem.

In raw sector map 100, either a virtual sector number or an “unused”value is used to indicate what is stored in each reserved sector 104.

An I/O operation status 102 is provided between raw sector map 100 andthe first reserved sector 104. I/O operation status 102 stores thecurrent state of NVFile 68 in case of a power failure or normal powercycle during an I/O operation. For example, I/O operation status 102 caninclude a flag indicating the type of operation (write, delete,compress, etc.) and then some additional data depending on thecontext/stage of the operation.

Since, as described below, compression will normally occur after everyfourth sector-write in this exemplary arrangement, seven reservedsectors 104 are employed to cache data in the very likely event that apower cycle will occur while the data are awaiting compression. Thus,all data from the file system is persisted somewhere while it is beingmoved.

The seven reserved sectors 104 include additional space for use duringdelete operations. For example, as part of a delete operation thecompressed block containing the deleted cluster must be decompressed andreassembled with a new fourth sector. To provide for safe/atomicoperation, all four sectors of that particular compressed block arestored in reserved sectors 104 until such time as the delete operationand recompression has been successfully completed.

The remaining space in NVRAM 32 is divided into 128-byte subsectorswhere compressed data blocks are stored. Each 128-byte subsector willbegin with a group ID 108 (or marked “unused”), as shown in greaterdetail in subsectors 106 a and 106 b. Group ID 108 will identify whichsubsectors 106 belong to which compressed block, since they will notnecessarily be written contiguously. In addition, as depicted insubsector 106 a, the first subsector of a compressed block within NVRAM32 will have, following the group ID 108, four virtual sector numbers110 to identify where the data belongs in the real file system.

FIG. 5 is an illustrative/functional block diagram file system databeing compressed and stored in subsectors 106. Here, it is assumed thatwrite requests #1, #2, and #3 have each been received and stored in rawsectors 0, 1, and 2, respectively. When write request #4 is subsequentlyreceived, all four data blocks are provided to a data compressorfunction 120 to produce a compressed block of data. The compressed blockof data is then provided to a splitter function that stores pieces A, Band C of the compressed data in unused subsectors 106.

The Sector Allocation Table (SAT) 36 is essentially the “glue” relatingthe compressed block subsectors 106 of NVRAM 32 to the Virtual SectorTable (VST) 38 that is presented to the file system. Group IDs 108 arestored in compressed subsectors to allow for generation of SAT 36 atboot-up/init time. SAT 36 is basically a fixed-size mirror of thecompressed-block subsectors 106 in NVRAM 32. There is one SAT entry foreach compressed subsector 106, and each one will either be marked“unused” or indicate the next compressed subsector 106 in the chain. Thelast member of a chain will point to itself to mark the end.

SAT information is not be stored directly to NVRAM 32, but ratherinferred at boot time using Group ID 108 and the Virtual Sector Numbers110 that are stored in every physical compressed subsector 106. TheGroup ID number and the sequential order in which subsectors having acommon Group ID 108 are written/read, will be used to generate thecompressed subsector chain information in SAT 36.

At boot-time, for example, each NVRAM subsector 106 is read, in orderfrom the beginning to the end of the subsector storage space. The firstbyte of each subsector contains either an “unused” value, or a Group ID108. For each unique Group ID 108, every following subsector 106 with amatching Group ID 108 will be associated with that first subsector 106.The resulting chain of associated subsectors 106, in the order found,will eventually comprise a compressed block that can be reassembled anddecompressed. For the first unique Group ID found, an entry is made inthe SAT that is later filled in with the offset address of the nextsubsector 106 in that group. When the final subsector 106 is found(determined only by reaching the end of the NVRAM and finding no moresubsectors in that group), the final SAT 36 entry is marked with its ownaddress, indicating the end of the chain.

As described above, instead of mapping FATFS sectors directly tolike-sized blocks of NVRAM 32, NVFile 68 presents VST 38 to FATFS whileactually storing compressed blocks of data in the actual NVRAMsubsectors 106. In order to minimize NVRAM overhead of this scheme, VST38 is generated on the fly from this information at boot time, ratherthan stored in NVRAM in its entirety. In addition, a small portion ofuncompressed data is stored in reserved raw sectors 104 of NVRAM 32 topersist sectors that have been written but not had a chance to compressyet.

To properly generate VST 38 at boot time, it is necessary to maintainand persist (during write operations) the relationship between thecompressed data blocks and the virtual sectors. This relation is storedin the table of Group IDs 40, which map virtual sectors to groups ofphysical compressed subsectors 106.

When a new group of four sectors is compressed, they are assigned anunused Group ID 108. A table is stored at the beginning of thecompressed data block, listing the virtual sector numbers represented bythe compressed block. This relationship between the Group ID, physicalsubsectors, and virtual sectors numbers, is maintained at runtime.During initialization, Group ID table 40 is therefore dynamicallygenerated, and maintained during all I/O operations.

By way of example, each entry in VST 38 can be a pointer to the firstSAT entry corresponding to that virtual sector. For each compressedblock containing four virtual sectors of data, there will be four VSTspointing to its first SAT entry. The I/O operation can then start fromthat SAT entry and simply “walk” the pointers to retrieve and reassemblethe entire compressed block.

The purpose of Group ID 108 is to store as little organizational (i.e.,non-data) information as possible in NVRAM. Every virtual sector in theVST must point to a compressed block, but since each compressed blockcontains four virtual sectors, otherwise unrelated virtual sectors willshare the Group ID they reside in.

When four sectors are compressed, the new compressed block is assignedthe next-unused Group ID 108 from the Group ID table 40 in RAM 34. GroupID 108 itself is saved as the first byte in each physical sector thatthe compressed block gets stored in.

During boot-up time, Group ID table 40 is re-created based on the storedGroup ID information. This can be accomplished by looping iterativelythough the NVRAM physical subsectors, matching up all of the sectorswith others sharing the same Group ID 108 to reestablish the associativerelationship. Then, the virtual sector numbers and Group Ids can belinked in the table in RAM 34.

FIG. 3 demonstrates how a sector write request from the file system isrouted through VST 38, and the data buffer is compressed and stored in acompressed block of NVRAM 32.

As shown in the example of FIG. 5, to increase the efficiency of thedata compression, four sectors are compressed at a time rather than justone. However, there is no guarantee that write operations will come infour-sector increments. As a result, a buffer is persisted which canstore uncompressed data that is waiting to be compressed. The first“line” of physical NVRAM (raw sectors “0”, “1”, and “2”) is reserved forthree raw sectors, and once those are filled they can be combined withthe fourth sector of incoming data, to produce a compressed block.

The compressed block will then be split so that it can fit into a numberof smaller physical memory subsectors 106. How many subsectors arerequired will depend on the size of the final compressed block. Piecesof the compressed block are then copied into NVRAM 32 and storedpersistently.

The location of free physical memory sectors may be determined using aniterative loop to find the next available unused subsector, if one isavailable. Since it is difficult to know ahead of time the final size ofa compressed block, it is preferable to allow for fragmentation to occurso as to make better use of the available memory space.

As part of the write operation, NVFile is also responsible formaintaining the integrity of the Group ID table 40. As well as updatingthe dynamic Group ID table 40 in RAM 34 to reflect the new writeoperation, it must also store the correct Group ID 108 info in thesubsectors 106 that are written.

After the compressed block is split into subsectors 106, they must bekept in order so that the original compressed block can be recreatedlater for decompression. From the beginning to the end of NVRAM 32,subsectors 106 belonging to any compressed block will be in order; therewill be no actual pointers stored in NVRAM 32 for purposes ofmaintaining subsector chains.

An incoming Read I/O operation will result in a hit on VST 38, whereactual file system sectors correspond to locations of NVRAM compressedblocks. Since multiple virtual sectors are stored in a single compressedblock, and the compressed block must be decompressed to retrieve data,the entire compressed block must be reassembled. Since this is true forany virtual sector residing within the block, virtual sectors will allpoint to the beginning of their respective compressed blocks. Furtheraddressing is stored in the compressed block header and decoded afterdecompression.

When a virtual sector hit point to any physical memory portion within acompressed block, the first memory portion is read, and the chainfollowed to each memory portion comprising the compressed block. Thecompressed block can then be reassembled in a RAM memory buffer,decompressed, and the resulting raw data returned to the file system.

There is a chance that a VST hit will point to an uncompressed rawsector 104 in the reserved line of physical NVRAM 32. In these cases,the uncompressed data will simply be read straight through and returnedto the file system.

When a virtual sector is deleted by FATFS, the compressed block in whichit resides is decompressed, and reassembled without the deleted data. Ifone or more uncompressed sectors are already waiting in the reservedarea 104, one of them can be combined with the remaining three from thecompressed block to write a new block of four sectors. However, theexisting compressed block cannot be deleted until a new one is written.In order to insure safe/atomic operation, it is important to reservefour additional uncompressed sectors 104 (i.e., raw sectors “3”, “4”,“5”, and “6”) in the worst case but likely event that the first line ofraw sectors 104 (i.e., raw sectors “0”, “1”, and “2”) are already fullwhen a cluster is deleted.

Deleted virtual sectors will be marked as unused in VST 38 and SAT 36,and their former Group ID 108 is marked “unused”.

A common scenario is to have a FATFS sector re-written with new data.This operation takes place in much the same way as the aforementioneddelete operation. The main difference is that instead of finding a newvirtual sector to replace the deleted one, a new compressed block andsubsector chain are stored using the new data from the updated sector.

FATFS 66 may also be modified to notify NVFile 68 via an IOCTL when aformat operation takes place. This way NVFile can mark all of theclusters as unused and reset all of the tables. It is important thatthis notification take place so that the status of the used versus freesectors is consistent between the file system and NVFile 68.

It should be understood that the methods and arrangements describedherein are not limited to data compression stages having compressionratios of 4:1, memory layouts having seven reserved sectors, raw sectorsof 512 bytes, or compressed sectors of 128 bytes. For example, one ormore of these parameters can be higher or lower depending upon thecomputing device.

Thus, although some preferred embodiments of the various methods andarrangements of the present invention have been illustrated in theaccompanying Drawings and described in the foregoing DetailedDescription, it will be understood that the invention is not limited tothe exemplary embodiments disclosed, but is capable of numerousrearrangements, modifications and substitutions without departing fromthe spirit of the invention as set forth and defined by the followingclaims.

1. A system comprising: means for receiving file system data; means forstoring the file system data in a plurality of reserved sectors within anon-volatile memory; means for compressing the file system data storedwithin the plurality of reserved sectors to create a compressed datablock; and means for storing the compressed data block in at least onephysical subsector within the non-volatile memory, wherein the physicalsubsector is associated with at least one virtual sector identifiablethrough sector allocation information stored in a volatile memory thatis operatively accessible by an operating system, wherein the means forreceiving file system data further includes means for presenting anoperating system with a plurality of operatively accessible virtualsectors resulting in a virtual memory capacity that exceeds the actualphysical capacity of the non-volatile memory, wherein the means forstoring the compressed data block in at least one physical subsectorwithin the non-volatile memory further includes means for mapping theplurality of virtual sectors to at least one physical subsector througha Virtual Sector Table (VST) stored in the volatile memory andpresenting the operating system with the VST, and wherein the means formapping the plurality of virtual sectors to at least one physicalsubsector through the Virtual Sector Table (VST) further includes meansfor providing a Sector Allocation Table (SAT) within the volatilememory, the SAT mapping the physical subsectors to the VST.
 2. Thesystem of claim 1, wherein the means for providing a Sector AllocationTable (SAT) within the volatile memory further includes means forgenerating the SAT based at least on a unique group identifier that isstored in each physical subsector associated with storing the compresseddata block.
 3. The system of claim 2, wherein the Sector AllocationTable (SAT) is generated during a device initialization time.
 4. Acomputing system comprising: one or more processors; one or morecomputer-readable media; and computer-readable instructions on the oneor more computer-readable media which, when executed by the one or moreprocessors, cause the one or more processors to perform acts comprising:receiving file system data; storing the file system data in a pluralityof reserved sectors within a non-volatile memory; compressing the filesystem data stored within the plurality of reserved sectors to create acompressed data block; and storing the compressed data block in at leastone physical subsector within the non-volatile memory, wherein thephysical subsector is associated with at least one virtual sectoridentifiable through sector allocation information stored in a volatilememory that is operatively accessible by an operating system, whereinreceiving file system data further includes presenting an operatingsystem with a plurality of operatively accessible virtual sectorsresulting in a virtual memory capacity that exceeds the actual physicalcapacity of the non-volatile memory, wherein storing the compressed datablock in at least one physical subsector within the non-volatile memoryfurther includes mapping the plurality of virtual sectors to at leastone physical subsector through a Virtual Sector Table (VST) stored inthe volatile memory and presenting the operating system with the VST,and wherein mapping the plurality of virtual sectors to at least onephysical subsector through the Virtual Sector Table (VST) furtherincludes providing a Sector Allocation Table (SAT) within the volatilememory, the SAT mapping the physical subsectors to the VST.
 5. Thecomputing system as recited in claim 4, wherein providing a SectorAllocation Table (SAT) within the volatile memory further includesgenerating the SAT based at least on a unique group identifier that isstored in each physical subsector associated with storing the compresseddata block.
 6. The computing system as recited in claim 5, wherein theSector Allocation Table (SAT) is generated during a deviceinitialization time.